Integrated single and twin screw extruder

ABSTRACT

An extruder is disclosed, and more particularly, to an integrated single screw extruder and a twin screw extruder for mixing, compounding, kneading and/or extruding of materials. The integrated extruder includes a first barrel assembly and a second barrel assembly. The integrated extruder further includes a first screw having a first threaded portion and a second threaded portion. The first threaded portion is housed within the first barrel assembly and is configured to provide upstream material processing. The second threaded portion is housed within the second barrel assembly and is configured to provide downstream material processing. The integrated extruder further includes a second screw having a non-threaded shaft portion and a threaded portion. The threaded portion of the second screw is housed within the second barrel assembly and is configured to provide the downstream material processing with the second threaded portion of the first screw.

FIELD OF THE INVENTION

The invention relates to an extruder and, more particularly, to anintegrated single screw extruder and a twin screw extruder for mixing,compounding, kneading and/or extruding of materials.

BACKGROUND OF THE INVENTION

Several techniques are available to process materials, including singlescrew extruders, twin screw extruders and batch mixers. Single screwextrusion is typically used for core operations in polymer processing. Agoal of a single screw extrusion process is to build pressure in apolymer melt so that it can be extruded through a die or injected into amold. Twin screw extrusion, on the other hand, is used extensively formixing, compounding, reacting and extruding materials. For example, twinscrew extruders can be used for processing many types of polymericmaterials; although other materials can also be processed with twinscrew extruders such as raw materials for food processing.

In operation, twin screw extruders have a profile for extrusion ofthermally sensitive materials (e.g., PVC) and specialty polymerprocessing operations, such as compounding, devolatilization, chemicalreactions, etc. Also, twin screw extruders exhibit improved processingcapabilities. For example, twin screw extruders can have intermeshing ornon-intermeshing screws along each of their entire length and throughoutthe housing, and can be designed as co-rotating or counter-rotating toachieve particular mixing characteristics. In this way, usingintermeshing screws, the twin screw extruders can offer improved feedingand more positive conveying characteristics, which allow the machine toprocess hard-to-feed materials (e.g., powders, slippery materials,etc.). The twin screw extruders also yield short residence times and anarrow residence time distribution (RTD). Also, the twin screw extrudersexhibit improved mixing, with larger heat transfer areas to allowimproved control of stock temperatures.

SUMMARY OF THE INVENTION

In a first aspect of the invention, an integrated extruder comprises afirst barrel assembly and a second barrel assembly. The integratedextruder further comprises a first screw having a first threaded portionand a second threaded portion. The first threaded portion is housedwithin the first barrel assembly and is configured to provide upstreammaterial processing. The second threaded portion is housed within thesecond barrel assembly and is configured to provide downstream materialprocessing. The integrated extruder further comprises a second screwhaving a non-threaded shaft portion and a threaded portion. The threadedportion of the second screw is housed within the second barrel assemblyand is configured to provide the downstream material processing with thesecond threaded portion of the first screw.

In another aspect of the invention, an integrated extruder comprises asingle screw barrel assembly and a twin screw barrel assembly detachablyaffixed to the single screw barrel assembly. The integrated extruderfurther comprises a first screw having a first threaded portion housedwithin the single screw barrel assembly and a second threaded portionhoused within the twin screw barrel assembly. The integrated extruderfurther comprises a second screw having a shaft portion and a threadedportion. The threaded portion of the second screw is housed within thetwin screw barrel assembly.

In yet another aspect of the invention, a method of processing materialcomprises: placing material within a hopper assembly for feeding into afirst housing having a single threaded portion of a screw; processingthe material within the first housing with the single threaded portion;transporting the processed material from the first housing to a secondhousing using the single threaded portion of the screw; furtherprocessing the processed material with a twin screw configurationcomprising a second threaded portion of the screw and a threaded portionof a second screw; and metering the material to a die with the twinscrew configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIG. 1 shows a perspective view of the twin screw extruder in accordancewith aspects of the present invention;

FIG. 2 shows an exploded view of the screws in accordance with aspectsof the present invention;

FIGS. 3a and 3b show the respective compartments (e.g., barrelassemblies) of the twin screw extruder in accordance with aspects of thepresent invention; and

FIGS. 4a and 4b show alternative respective compartments (e.g., barrelassemblies) of the twin screw extruder in accordance with aspects of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to an extruder and, more particularly, to anintegrated single screw extruder and twin screw extruder for mixing,compounding, kneading and/or extruding of materials. In embodiments, thepresent invention can be operated as a single screw extruder or a twinscrew extruder, without the need to have two separate extruders. Asshould be understood by those of skill in the art, the configuration ofthe present invention is very economical due to capital cost reduction.

In embodiments, the present invention combines a single screwconfiguration and twin screw configuration into a single extrudermachine. For example, in embodiments, a first barrel assembly is used tohouse a single screw configuration and a second barrel assembly is usedto house a twin screw configuration. Advantageously, the barrelassemblies are configured to separate from one another, so that thesingle screw configuration can be used alone. Also, as it should beunderstood by those of ordinary skill in the art, in conventionalextruders, there are several extruding zones: solid conveying,transition, melting and kneading, and metering; however, in the extruderof the present invention, there is no need to provide two screws toconvey and transit molten polymers to the kneading section. Instead, inthe extruder of the present invention, a single screw can be used toconvey and transit molten polymers (or other materials) to the kneadingsection, i.e., twin screw extruder.

In embodiments, the extruder of the present invention can be used as acompounder, mixer and a reactor. In embodiments, the extruder can beused for processing many types of materials. These materials can be, forexample, polymeric and plastic materials, as well as raw materials forfood processing. Of course, other material processes are alsocontemplated by the present invention. Also, advantageously, asdescribed in more detail below, the extruder of the present inventionsignificantly reduces material costs, and provides a simplifiedconfiguration, compared to conventional screw extruders.

FIG. 1 shows a perspective view of the extruder in accordance withaspects of the present invention. More specifically, the extruder 10includes a barrel assembly 25, comprising a single screw barrel assembly25 a (which houses a single screw 20 a) and a twin screw barrel assembly25 b (which houses twin screws 20 a, 20 b). As shown in this exemplaryconfiguration, a motor and drive system 15 drive screws 20 a, 20 b whichare housed within the respective screw barrel assemblies 25 a, 25 b. Themotor and drive system 15 include a plurality of gears 30 driven bymotor 35 which, in turn, drive the screws 20 a, 20 b. As one of ordinaryskill in the art should understand, the motor and drive system 15 canhave many different configurations, and can provide variable drive ratesfor the screws 20 a, 20 b. For example, the motor and drive system 15can provide both co-rotation and counter-rotation of the screws 20 a, 20b.

More specifically, the barrel assembly 25 includes two separate,adjacent compartments (e.g., barrel assemblies) 25 a, 25 b. Inembodiments, the barrel assembly 25 a is positioned between the motorand drive system 15 (i.e., plurality of gears 30) and the barrelassembly 25 b. That is, the barrel assembly 25 a is at an upstreamprocessing of the extrusion process; whereas, the barrel assembly 25 bis positioned at downstream processing of the extrusion process. Inembodiments, the barrel assemblies 25 a, 25 b can be separated by aswivel arm or other mechanism 100, in order to convert the extruder intoa single extruder or combination of a single and twin screw extruder. Inillustrative, non-limiting examples, the twin screw barrel assembly 25 bcan be separated or detached from the single screw barrel assembly 25 ausing the swivel arm, servo motors, rack and pinion gears, etc., all ofwhich are represented by reference numeral 100. In embodiments, the twinscrew barrel assembly 25 b can be coupled to the single screw barrelassembly 25 a by a hinge, also at reference numeral 100. In this way,the extruder of the present invention can function as either a singlescrew extruder (by removing the twin screw barrel assembly 25 b) or as atwin screw extruder (by coupling together the screw barrel assemblies 25a, 25 b).

As further shown in FIG. 1, in embodiments, the screw 20 a can includetwo detachable threaded portions 20 a′ and 20 a″ provided in therespective screw barrel assemblies 25 a, 25 b. The detachable threadedportions 20 a′ and 20 a″ can be coupled together using any conventionalcoupling mechanism 20 a′″. For example, the coupling mechanism 20 a′″can be a grooved mating surface, provided on adjoining ends of thedetachable threaded portions 20 a′ and 20 a″. The threaded portion 20 a′is provided in the single screw barrel assembly 25 a (for upstreamprocessing), and the threaded portion 20 a″ is provided in the twinscrew barrel assembly 25 b (for downstream processing).

In contrast, the screw 20 b can include a threaded portion 20 b′ andnon-threaded portion (e.g., shaft) 20 b″, which are coupled togetherusing any conventional coupling mechanism 20 a′″. Similar to above, thecoupling mechanism 20 a′″ can be a grooved mating surface, provided onadjoining ends of the components 20 b′ and 20 b″. In embodiments, theshaft 20 b″ can be hollow and devoid of screw elements, for example, inorder to save material costs. Also, as should be understood from FIG. 1,the shaft 20 b″ is provided in the single screw barrel assembly 25 a;whereas, the threaded portion 20 b′ is housed with the threaded portion20 a″, in the twin screw barrel assembly 25 b.

In the twin screw barrel assembly 25 b, both screws 20 a, 20 b arethreaded (e.g., twin screw configuration), which can be intermeshed ornon-meshed, depending on the specific configuration of the presentinvention. In embodiments, the screw pattern of the threaded portions ofthe screws 20 a, 20 b can also include different thread configurationswithin the twin screw barrel assembly 25 b, as further shown in FIG. 2.For example, the screw pattern can be a kneading block screw element, asone illustrative, non-limiting example. The screws 20 a, 20 b can berotated either clockwise or counter clockwise.

In embodiments, the single screw barrel assembly 25 a is a conveyingcompartment, which is used to house the thread portion 20 a′ and shaft20 b″ of the screw 20 b. In embodiments, the single screw barrelassembly 25 a is designed to convey material fed from a hopper and feedsystem 45 to the adjacent twin screw barrel assembly 25 b. The singlescrew barrel assembly 25 a can also be used as a transition compartment.For example, heating of the material can begin in the single screwbarrel assembly 25 a through, for example, shearing friction and/orheaters. In embodiments, the threaded portion 20 a′ of screw 20 a caninclude a conveying, transition, melting and metering zone, as should beunderstood by those of ordinary skill in the art.

The twin screw barrel assembly 25 b, on the other hand, may be akneading compartment, adjacent and in material flow communication withthe single screw barrel assembly 25 a. In embodiments, the kneadingcompartment can be a bi-lobule or tri-lobule kneading compartment. Asdescribed herein, material can be mixed, kneaded, heated, melted,metered, etc. within the twin screw barrel assembly 25 b, using the twothreaded portions 20 a″, 20 b′ of the respective screws 20 a, 20 b. Inembodiments, the twin screw barrel assembly 25 b will transit materialto a die 50. As should be understood by those of skill in the art, thedie 50 can include any combination of arrangements, for extrudingdifferent shapes.

In embodiments, the die 50 can be mounted to either the single screwbarrel assembly 25 a or the twin screw barrel assembly 25 b, dependingon the application of the extruder as a single screw extruder or adouble screw extruder. For example, in the single screw extruderconfiguration, the die 50 can be removed from the twin screw barrelassembly 25 b and directly mounted to the single screw barrel assembly25 a.

As optional components, the barrel assembly 25 can include heaters 35′,as well as a cooling system 40. The heaters 35′ are designed to heatmaterial conveyed and kneaded within the barrel assembly 25. This willassist in the shearing of the material, as should be understood by thoseof skill in the art. An optional vent and vacuum port 55 can also beprovided on the barrel assembly 25, preferably at the twin screw barrelassembly 25 b. The vent and vacuum port 55 can be used to vent gasesfrom the melt.

FIG. 2 shows an exploded view of the screws 20 a, 20 b in accordancewith aspects of the present invention. As shown in FIG. 2, screw 20 ahas a length “X”, which is substantially fully threaded and which can begreater than, less than or equal to the length “Y” of screw 20 b. Asshould be understood by those of skill in the art, in embodiments, thelength “X” of screw 20 a may correspond to the length of the barrelassembly 25 of FIG. 1. Also, as shown in FIG. 2, the screw 20 b has athreaded portion 20 b′ and a shaft portion 20 b″ devoid of any threadedelements. In embodiments, the shaft portion 20 b″ can be hollow, as itdoes no kneading, conveying, etc. of the material. In this way,additional material costs can be saved.

As further shown in FIG. 2, the screws 20 a, 20 b each include thecoupling mechanism 20 a′″. As discussed above, the coupling mechanism 20a′″ couples together the different portions of the screws 20 a, 20 b, inthe twin extruder configuration of the present invention, i.e., when thesingle screw barrel assembly 25 a and twin screw barrel assembly 25 bare connected together. Similarly, the screws 20 a, 20 b can bedecoupled from one another by the coupling mechanism 20 a′″, in thesingle extruder configuration of the present invention, i.e., when thetwin screw barrel assembly 25 b is swiveled away from the single screwbarrel assembly 25 a.

As discussed above, the shaft portion 20 b″ will reside in the singlescrew barrel assembly 25 a of FIG. 1 with the threaded portions 20 a′,so that only a single threaded screw is present. On the other hand, thethreaded portion 20 b′ of screw 20 b is configured to extend within thetwin screw barrel assembly 25 b, with the threaded portion 20 a″ of thescrew 20 a′. In this way, threaded portions of the screws 20 a, 20 bwill be provided in the twin screw barrel assembly 25 b; whereas, onlythe threaded portion of the screw 20 a will be present in the singlescrew barrel housing assembly 25 a.

FIGS. 3a and 3b show the respective barrel assemblies 25 a, 25 b, inaccordance with aspects of the present invention. As shown in theserepresentations, the barrel assemblies 25 a, 25 b are of a cylindricalshape. More specifically, FIG. 3a shows an exploded view of the singlescrew barrel assembly 25 a. As shown in this representation, the singlescrew barrel assembly 25 a includes a hole 25 a′, for accommodating thethreaded portion 20 a′ of screw 20 a. The single screw barrel assembly25 a includes a hollow section 25 a″, for accommodating the shaftportion 20 b″ of the screw 20 b. As an example, the hollow section 25 a″is only a cover.

FIG. 3b shows an exploded view of the twin screw barrel assembly 25 b.As shown in this representation, the twin screw barrel assembly 25 bincludes a two hole configuration 25 b′ (e.g., similar to a FIG. 8design), for accommodating the threaded screw 20 a and the threadedportion 20 b′ of the screw 20 b.

FIGS. 4a and 4b show alternative respective barrel assemblies 25 a and25 b, in accordance with aspects of the present invention. As shown inthese representations, the barrel assemblies 25 a, 25 b are of arectangular or square shape. More specifically, FIG. 4a shows anexploded view of single screw barrel assembly 25 a. As shown in thisrepresentation, the single screw barrel assembly 25 a includes a hole 25a′, for accommodating the threaded screw 20 a. The single screw barrelassembly 25 a also includes a hollow section 25 a″ for accommodating theshaft portion 20 b″ of the screw 20 b. As an example, the hollow section25 a″ is only a cover.

FIG. 4b shows an exploded view of the twin screw barrel assembly 25 b.As shown in this representation, the twin screw barrel assembly 25 bincludes a two hole configuration 25 b′ (e.g., similar to a FIG. 8design), for accommodating the threaded portions of both screws 20 a, 20b.

In operation, materials in the form of plastic pellets or powders, food,and others types are material are fed into the hopper 45, where they areconveyed and introduced to first portion of the single screw 20 a(within the single screw barrel assembly 25 a). Depending on theoperating conditions, materials will then transit to the melting zone(for polymers or plastics). The L/D ratio of the single screw 20 awithin the single screw barrel assembly 25 a may vary depending on thematerial specifications. At the final portion of the threaded portions20 a′ of the single screw 20 a, materials will be metered to the twinscrew barrel assembly 25 b, where the threaded portions of the screws 20a, 20 b can process the material, e.g., mixing, compounding, kneading.The L/D ratio of the twin-screw section may also vary upon materialspecifications. Finally, the material will pass through the die 50 whereit is taking off by conventional take-off machinery (e.g., apellitizer).

In embodiments, when only the single screw extruder is used, it ispossible to remove the twin screw barrel assembly 25 b, and set it asideby using the mechanism 100. In this case, the tip of the threadedportions 20 a′ of the single screw 20 a can be covered with a cap groove(also represented by reference numeral 20′″), e.g., a female groovedcap. The die 50 can then be mounted to the single screw barrel assembly25 a, so that the extruder machine can operate as single screw extruder.

Accordingly and advantageously, the present invention provides asimplified design compared to existing complicated screw extruders. Thatis, the present invention is able to significantly reduce materialcosts, as well as efficiently integrate a single screw and twin screwextruder together. Also, by using this simplified design, the presentinvention advantageously saves screw materials. Moreover, andimportantly, it is now possible to simply use a single screwconfiguration to transit molten materials, e.g., polymers, etc., to thekneading section, e.g., twin screw configuration within the twin screwbarrel assembly.

Also, as it should be understood by those of ordinary skill in the art,in conventional extruders, there are several extruding zones: solidconveying, transition, melting and kneading, and metering; however, inthe extruder of the present invention, there is no need to provide twoscrews to convey and transit molten polymers to the kneading section.Instead, in the extruder of the present invention, a single screw can beused to convey and transit molten polymers (or other materials) to thekneading section, i.e., twin screw extruder.

The foregoing examples have been provided for the purpose of explanationand should not be construed as limiting the present invention. While thepresent invention has been described with reference to an exemplaryembodiment, changes may be made, within the purview of the appendedclaims, without departing from the scope and spirit of the presentinvention in its aspects. Also, although the present invention has beendescribed herein with reference to particular materials and embodiments,the present invention is not intended to be limited to the particularsdisclosed herein; rather, the present invention extends to allfunctionally equivalent structures, methods and uses, such as are withinthe scope of the appended claims.

What is claimed:
 1. An integrated extruder comprising: a single screwbarrel assembly defining a conveying compartment housing a firstthreaded portion of a first screw and a non-threaded shaft portion of asecond screw; a twin screw barrel assembly detachably affixed to thesingle screw barrel assembly and defining a conveying compartmenthousing a second threaded portion of the first screw and a threadedportion of the second screw, the second threaded portion of the firstscrew and the threaded portion of the second screw detachably coupled tothe first threaded portion and non-threaded shaft portion, respectively;and a die configured to mount to the twin screw barrel assembly in adouble screw configuration of the extruder in which the single and twinscrew barrel assemblies are affixed and to the single screw barrelassembly in a single screw configuration of the extruder in which thesingle and twin screw barrel assemblies are detached.
 2. The extruder ofclaim 1, wherein in the double screw configuration, the single screwbarrel assembly is upstream from the twin screw barrel assembly.
 3. Theextruder of claim 1, wherein in the double screw configuration: thefirst threaded portion of the first screw provides upstream processingof a molten material including transit of the molten material to thetwin screw barrel assembly; and the second threaded portion of the firstscrew and the threaded portion of the second screw provide downstreamprocessing of the material.
 4. The extruder of claim 1, wherein thedetachable affixing of the twin screw barrel assembly is provided by oneof a servo motor, a swivel arm, and a rack and pinion gear.
 5. Theextruder of claim 1, wherein the shaft portion of the second screw is anon-threaded hollow shaft.
 6. The extruder of claim 1, wherein: thefirst threaded portion and the second threaded portion of the firstscrew are configured to couple together by a mating surface; the shaftportion and the threaded portion of the second screw are configured tocouple together by a mating surface; the first threaded portion and thesecond threaded portion of the first screw are configured to decouplefrom one another when the single screw barrel assembly and the twinscrew barrel assembly are detached from one another; and the shaftportion and the threaded portion of the second screw are configured todecouple from one another when the single screw barrel assembly and thetwin screw barrel assembly are detached from one another.
 7. Theextruder of claim 1, further comprising a cap configured to cover an endof the first threaded portion of the first screw when the first threadedportion and the second threaded portion of the first screw are decoupledfrom one another.
 8. A method comprising: providing the integratedextruder of claim 1 in the single screw configuration; converting theextruder from the single screw configuration to the double screwconfiguration; placing material within a hopper assembly feeding thematerial into the compartment of the single screw barrel assembly;processing the material within the single screw barrel assembly by thefirst threaded portion; transporting the processed material from thesingle screw barrel assembly to the twin screw barrel assembly using thefirst threaded portion of the first screw; further processing theprocessed material using the second threaded portion of the first screwand the threaded portion of the second screw; and metering the materialto the die using the twin screw barrel assembly.
 9. The method of claim8, wherein: the first threaded portion of the first screw providesupstream processing of the material in a molten state including transitof the molten material to the twin screw barrel assembly; and the secondthreaded portion of the first screw and the threaded portion of thesecond screw provide said further processing of the material in themolten state downstream of the single screw barrel assembly.